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I´m doing a parasitic draw test on my car battery, in order to check the draw with the car locked and alarmed I need to use the COM and 20a sockets of the Multimeter, if I use the COM and mA sockets the battery doesnt make a circuit (car dead). Whats the mA reading on the Multimeter, 240 mA??enter image description here

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    \$\begingroup\$ no, that's 0.24 mA. \$\endgroup\$ – Marcus Müller Jan 10 at 13:56
  • \$\begingroup\$ thanks Marcus - so, even with the probes in COM and 20A, the reading of 0.24 (approx a quarter of a mA) is correct? \$\endgroup\$ – Steve Dunn Jan 10 at 14:06
  • \$\begingroup\$ Hi Steve, yes it would most likely be a good estimate. Just remember that in most cases the off the shelf multimeters are not extremely accurate when it comes to very low currents are these multimeters have their own resistance that comes in the way. \$\endgroup\$ – Nouman Qaiser Jan 10 at 14:10
  • \$\begingroup\$ @SteveDunn I don't know the manual to your multimeter - but for such low currents, it's not wrong to switch to the lower-amperage connector. \$\endgroup\$ – Marcus Müller Jan 10 at 14:12
  • \$\begingroup\$ You asked if 0.24mA "is correct". That value is a correct interpretation of the meter's display, but it may not be an accurate measurement of the current. \$\endgroup\$ – Elliot Alderson Jan 10 at 20:36
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Most likely here is what is happening.

The fuse for the mA circuit in your meter is blown and that is why it is not making a connection with the red lead in the mA plug.

With the lead of the meter in the 20A plug, only when the dial is set to A do you get a valid reading. With the red lead in the 20A plug and the dial set to mA the reading that you see is just noise, not a valid reading.

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  • \$\begingroup\$ Ah yes, the problem using the COM and mA probe sockets is that as soon as its placed into the car´s battery circuit it overloads, blows the fuse and sets off the cars alarm. I think I´ve found a way of doing it - connect one Meter (COM and 20A) to complete the battery circuit AND another Meter (COM and mA) but switched off. When the cars alarm is set, the system shuts down the reduces the draw in stages, once the higher range Meter reports a negligible draw, switch on the secon Meter and measure mA. Any thoughts? \$\endgroup\$ – Steve Dunn Jan 10 at 14:45
  • \$\begingroup\$ @SteveDunn That would work with two modifications. No need to switch meters on and off. The shunt in the meter is always live. Also, once the reading is manageable, disconnect the 20A meterall together because having it in circuit will shunt some current around the other meter. Finally, have you thought about investing in a battery disconnect switch? It goes in series with the negative terminal and has places for a meter to connect. \$\endgroup\$ – vini_i Jan 10 at 16:32
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    \$\begingroup\$ Yes, I have a battery isolator fitted as a temp solution to the battery drain, it also helps when metering. I´ll hook up the 2 x meters (with your suggested mods) and see how it goes. Thanks \$\endgroup\$ – Steve Dunn Jan 10 at 16:50
  • \$\begingroup\$ If you start with the meter switched off and switch to mA with 12 V on the test leads you risk destroying all the mV, resistance, diode, capacitance and uA ranges as you rotate the switch. \$\endgroup\$ – Transistor Jan 10 at 18:01
  • \$\begingroup\$ So, perhaps activate the second meter by plugging in the meter probe whilst its pre-set to mA? \$\endgroup\$ – Steve Dunn Jan 11 at 9:59

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